The quake's epicentre was in northern Nagano prefecture in central Japan, and tremor occurred at around 10:29 a.m. (0129 GMT) at a depth of around 10 km (6 miles), the weather agency said.

No abnormalities have been observed at Tokyo Electric Power Company Holdings' (TEPCO) Kashiwazaki-Kariwa nuclear power plant in neighboring Niigata prefecture, public broadcaster NHK quoted the electric utilities as saying. (Reporting by Kiyoshi Takenaka; Editing by Simon Cameron-Moore)